1. Field of the Invention
This invention relates to improvements in a continuously variable transmission incorporating therein a toroidal type continuously variable transmission utilized, for example, as a transmission for an automobile, and particularly to a continuously variable transmission in which the durability of the constituent members of a toroidal type continuously variable transmission can be secured.
2. Related Background Art
It has been studied to use a toroidal type continuously variable transmission as schematically shown in FIGS. 6 and 7 of the accompanying drawings, for example, as a transmission for an automobile. This toroidal type continuously variable transmission is such that as disclosed, for example, in Japanese Laid-Open Utility Model Application No. 62-71465, an input side disc 2 which is a first disc is supported concentrically with an input shaft 1 and an output side disc 4 which is a second disc is fixed to the end portion of an output shaft 3 disposed concentrically with the input shaft 1. Inside a casing containing the toroidal type continuously variable transmission therein, there are provided trunnions 6 pivotally movable about pivots 5 lying at twisted positions relative to the input shaft 1 and the output shaft 3.
The pivots 5 are provided on the outer sides of the opposite end portions of each of these trunnions 6. Also, the base end portions of displacement shafts 7 are supported on the central portions of the trunnions 6, and the trunnions 6 are pivotally moved about the pivots 5, whereby the angle of inclination of each displacement shaft 7 is made adjustable. Power rollers 8 are rotatably supported about the displacement shafts 7 supported by the trunnions 6. These power rollers 8 are sandwiched between the input side disc 2 and the output side disc 4. The inner sides 2a and 4a of the input side and output side discs 2 and 4 which are opposed to each other have their cross-sections forming concave surfaces obtained by an arc centering about the pivot 5 being rotated. The peripheral surfaces 8a of the power rollers 8 formed into spherical convex surfaces are made to bear against the above-mentioned inner sides 2a and 4a.
A loading cam type pressing device 9 is provided between the input shaft 1 and the input side disc 2, and by this pressing device 9, the input side disc 2 is resiliently pressed toward the output side disc 4. This pressing device 9 is comprised of a cam plate 10 rotatable with the input shaft 1, and a plurality of (e.g. four) rollers 12 held by a holder 11. A cam surface 13 which is an uneven surface extending in the circumferential direction is formed on one side (the left side as viewed in FIGS. 6 and 7) of the cam plate 10, and a similar cam surface 14 is also formed on the outer side (the right side as viewed in FIGS. 6 and 7) of the input side disc 2. The plurality of rollers 12 are supported for rotation about radial axes relative to the center of the input shaft 1.
When during the use of the toroidal type continuously variable transmission constructed as described above, the cam plate 10 is rotated with the rotation of the input shaft 1, the plurality of rollers 12 are pressed against the cam surface 14 on the outer side of the input side disc 2 by the cam surface 13. As a result, the input side disc 2 is pressed against the plurality of power rollers 8 and at the same time, the plurality of rollers 12 come into meshing engagement with the pair of cam surfaces 13 and 14, whereby the input side disc 2 is rotated. The rotation of this input side disc 2 is transmitted to the output side disc 4 through the plurality of power rollers 8, and the output shaft 3 fixed to this output side disc 4 is rotated.
When the rotational speed of the input shaft 1 and the output shaft 3 is to be changed and a speed reduction is to be effected between the input shaft 1 and the output shaft 3, the trunnions 6 are pivotally moved about the pivots 5 and the displacement shafts 7 are inclined so that as shown in FIG. 6, the peripheral surfaces of the power rollers may bear against that portion of the inner side 2a of the input side disc 2 which is toward the center and that portion of the inner side 4a of the output side disc 4 which is toward the outer periphery. When conversely, a speed increase is to be effected, the trunnions 6 are pivotally moved and the displacement shafts 7 are inclined so that as shown in FIG. 7, the peripheral surfaces 8a of the power rollers 8 may bear against that portion of the inner side 2a of the input side disc 2 which is toward the outer periphery and that portion of the inner side 4a of the output side disc 4 which is toward the center. If the angle of inclination of the displacement shafts 7 is made medium between FIG. 6 and FIG. 7, there will be obtained a medium transmission ratio between the input shaft 1 and the output shaft 3.
It is described in Japanese Laid-Open Patent Application Nos. 1-169169 and 1-312266 that when the toroidal type continuously variable transmission constructed and acting as described above is to be incorporated into a continuously variable transmission for an actual automobile, it is combined with a planetary gear mechanism. That is, during low speed running, the drive force of an engine is transmitted by only the toroidal type continuously variable transmission and during high speed running, the drive force is transmitted by the planetary gear mechanism, whereby a reduction in the torque applied to the toroidal type continuously variable transmission during high speed running may be achieved. With such a construction, the durability of each constituent member of the toroidal type continuously variable transmission can be improved.
In the case of the structure described in Japanese Laid-Open Patent Application Nos. 1-169169 and 1-312266, two sets of planetary gear mechanisms are incorporated and therefore, not only the structure becomes complicated and the cost runs up, but the installation space increases. Therefore, this structure is unsuitable as a continuously variable transmission for a small automobile or an FF vehicle which requires a transmission to be installed in a limited space near an engine room.